Passive power distribution for multiple electrode inductive plasma source

ABSTRACT

Systems, methods, and Apparatus for controlling the spatial distribution of a plasma in a processing chamber are disclosed. An exemplary system includes a primary inductor disposed to excite the plasma when power is actively applied to the primary inductor; at least one secondary inductor located in proximity to the primary inductor such that substantially all current that passes through the secondary inductor results from mutual inductance through the plasma with the primary inductor. In addition, at least one terminating element is coupled to the at least one secondary inductor, the at least one terminating element affecting the current through the at least one secondary inductor so as to affect the spatial distribution of the plasma.

PRIORITY

This application is a continuation of U.S. patent application Ser. No.12/698,007, entitled Passive Power Distribution for Multiple ElectrodeInductive Plasma Source, which claims priority to provisionalapplication No. 61/149,187, filed Feb. 2, 2009, entitled PASSIVE POWERDISTRIBUTION FOR MULTIPLE ELECTRODE INDUCTIVE PLASMA SOURCE.

FIELD OF THE INVENTION

The present invention relates generally to plasma processing. Inparticular, but not by way of limitation, the present invention relatesto systems, methods and apparatuses for applying and distributing powerto a multiple electrode inductive plasma processing chamber.

BACKGROUND OF THE INVENTION

Inductively coupled plasma processing systems are utilized to perform avariety of processes including etching processes and chemical vapordeposition processes. In many typical implementations, inductive coilantennas are wound around a reactive chamber and actively driven by RFpower so as to prompt ignition of (and to maintain) a plasma in thechamber.

Systems have been developed to utilize a single generator to drive twocoil antennas. In these systems, a generator is typically coupled (e.g.,through an RF match) to the first coil and a series capacitor couplesthe first coil to the second coil so that the two coils are bothactively driven by the generator (e.g., actively driven through an RFimpedance match).

SUMMARY OF THE INVENTION

Exemplary embodiments of the present invention that are shown in thedrawings are summarized below. These and other embodiments are morefully described in the Detailed Description section. It is to beunderstood, however, that there is no intention to limit the inventionto the forms described in this Summary of the Invention or in theDetailed Description. One skilled in the art can recognize that thereare numerous modifications, equivalents and alternative constructionsthat fall within the spirit and scope of the invention as expressed inthe claims.

One embodiment of the invention may be characterized as a system forcontrolling the spatial distribution of plasma in a processing chamber.The system in this embodiment includes a primary inductor disposed toexcite the plasma when power is actively applied to the primaryinductor; at least one secondary inductor located in proximity to theprimary inductor such that substantially all current that passes throughthe secondary inductor results from mutual inductance through the plasmawith the primary inductor; and at least one terminating element coupledto the at least one secondary inductor, the at least one terminatingelement affecting the current through the at least one secondaryinductor so as to affect the spatial distribution of the plasma.

Another embodiment may be characterized as a method for controlling aspatial distribution of plasma in a processing chamber that includes aprimary inductor and N secondary inductors. The method includes excitingthe plasma in the processing chamber with the primary inductor;inductively coupling the primary inductor to each of N secondaryinductors through the plasma, wherein N is equal to or greater than one;and terminating each of the N secondary inductors such thatsubstantially all current that passes through each of the N secondaryinductors results from mutual inductance through the plasma with theprimary inductor, the current through each of the N secondary inductorsaffecting the spatial distribution of the plasma.

Yet another embodiment of the invention may be characterized as anapparatus for controlling the spatial distribution of plasma in aprocessing chamber. The apparatus includes a primary terminal configuredto couple to, and actively apply power to, a primary inductor of theplasma processing chamber; a secondary terminal configured to couple toa corresponding secondary inductor of the plasma processing chamber; anda terminating element coupled to the secondary terminal, the terminatingelement disposed to provide a path for current flowing through thesecondary inductive component, wherein substantially all the currentthat passes through the secondary inductor and the terminating elementresults from mutual inductance through the plasma with the primaryinductor.

BRIEF DESCRIPTION OF THE DRAWINGS

Various objects and advantages and a more complete understanding of thepresent invention are apparent and more readily appreciated by referenceto the following Detailed Description and to the appended claims whentaken in conjunction with the accompanying Drawings wherein:

FIG. 1 is a block diagram depicting an exemplary embodiment of theinvention;

FIG. 2 is a block diagram depicting another exemplary embodiment of theinvention;

FIG. 3 is a block diagram depicting yet another embodiment of theinvention; and

FIG. 4 is a flowchart depicting a method that may be traversed inconnection with the embodiments described with reference to FIGS. 1-3.

DETAILED DESCRIPTION

Referring now to the drawings, where like or similar elements aredesignated with identical reference numerals throughout the severalviews, and referring in particular to FIG. 1, shown is aninductively-coupled plasma processing system 100 including a primarycoil 102 that is actively driven by a generator 104 (via a match 106) toignite and sustain a plasma 108 in a plasma processing chamber 110. Asdepicted, the exemplary system 100 includes N secondary coils L_(1-N)that are inductively coupled to the plasma 108, and the plasma 108 isinductively coupled to the primary coil 102. As a consequence, thesecondary coils L_(1-N) are inductively coupled to the primary coil 102via the plasma 108 so that power is applied to the secondary coilsL_(1-N) by the plasma 108.

As depicted, coupled to each of the N secondary coils L_(1-N) are acorresponding one of N passive elements 112 _(1-N), which passivelyterminate each of the N secondary coils L_(1-N). This architecture isvery different from known techniques (such as described above) that relyon actively driving each coil L_(1-N). Beneficially, because thesecondary inductors are not actively driven, the secondary coils may beplaced about the chamber 110 with added ease and plasma spatialuniformity control is more conveniently achieved since the secondaryinductors L_(1-N) are driven by mutual coupling, through the plasma 108,to the primary coil 102, and as a consequence, lack the need for adirect power feed. Multiple secondary coils can be added in this mannerbeyond what is practical for adding multiple directly-powered secondarycoils due to the inherent complexity and cost of additional poweredfeeds. Thus, plasma density may be manipulated in a more cost effectivemanner.

In operation, power is applied through the match 106 to the primary coil102, which effectively applies power to the chamber 110, and onceignited, the plasma 108 effectively operates as a secondary of atransformer, and the current that is induced in the plasma 108 inducescurrent in the secondary coils L_(1-N). In turn, the current that isinduced in the secondary coils L_(1-N), induces current in the plasma108 and affects the density of the plasma 108 in the regions proximateto each of the secondary coils L_(1-N).

The N passive elements 112 _(1-N), depicted as variable capacitors inthe exemplary embodiment, enable the current through each of the N coilsL_(1-N) to be regulated; thus enabling the ratio of current between theprimary 102 and the N secondary coils L_(1-N) to be regulated. As aconsequence, the plasma densities in regions proximate to each of theprimary 102 and secondary coils L_(1-N) may be regulated.

The generator 104 may be a 13.56 MHz generator, but this is certainlynot required and other frequencies are certainly contemplated. And thematch 106 may be realized by a variety of match network architectures.As one of ordinary skill in the art will appreciate, the match 106 isused to match the load of the plasma 108 to the generator 104. Bycorrect design of the matching network 106 (either internal to thegenerator or external as shown in FIG. 1), it is possible to transformthe impedance of the load to a value close to the desired load impedanceof the generator.

Referring next to FIG. 2, shown is an exemplary embodiment in which thepassive element (e.g., variable capacitor) and the match are bothpositioned within the same housing 220. As shown, at or near the housing220 is a primary terminal 221 that is coupled to a first outputconductor 222 that couples the generator 204 (through the match 206 andprimary terminal 221) to a primary coil 202. And a secondary terminal223, positioned at or near the housing 220, is coupled to a secondoutput conductor 224 that couples a passive termination element 212 andsecondary terminal 223 to a secondary coil 213. In addition, a controlportion 226 (also referred to herein as a controller) is disposed toreceive signals 228, 230 indicative of current levels (which areindicative of the density of the plasma 108 in the regions proximate tothe coils 202, 213) in the first 222 and second 224 output conductorsfrom first 232 and second 234 sensors (e.g., current transducers),respectively. And the control portion 226 is also arranged to control avalue (e.g., capacitance) of the passive element 212 (e.g., variablecapacitor).

In variations of the embodiment depicted in FIG. 2, instead of currentsensors 232, 234 (or in addition to current sensors 232, 234) othersensing components (either within or outside of the housing 220) may beused to provide an indication of the plasma density in close proximityto the coils 213. For example, optical sensors may be used to senseplasma properties (e.g., plasma density).

It should be recognized that the depicted components in FIG. 2 islogical and not intended to be a hardware diagram. For example, thecontrol portion 226 and the sensors 232, 234 may each be realized bydistributed components, and may be implemented by hardware, firmware,software or a combination thereof. In many variations of the embodimentdepicted in FIG. 2, the sensed current levels are converted to a digitalrepresentation, and the controller 226 uses the digital representationof the current signals 228, 230 to generate a control signal 235 todrive the passive element 212. In addition, the match 206 may becontrolled by the control portion 226 or may be separately controlled.

It should also be recognized that, for simplicity, only one secondarycoil 213 and one passive termination element 212 are depicted, but it iscertainly contemplated that two or more secondary coils 213 may beimplemented in connection with two or more passive termination elements212 (e.g., two or more passive termination elements housed with thematch).

In operation, the generator 204 applies power, through the match 206, tothe primary coil 202 and the current in the primary coil 202 (which issensed by the first sensor 232) induces current in the plasma 108, whichin turn, induces current in the secondary coil 213. And the currentflowing through the secondary coil 213, and hence the second outputconductor 224 and secondary terminal 223, is sensed by the second sensor234. As discussed with reference to FIG. 1, unlike prior artimplementations, the power that is applied by the secondary coil 213 tothe plasma 108 is derived from current flowing through the primary coil202. More particularly, the secondary coil 212 obtains power from theprimary coil 202 through the plasma 108.

The control portion 226, sensors 232, 234, and passive element(s) 212collectively form a control system to control aspects of the plasma(e.g., the spatial distribution of the plasma). The control portion 226in this embodiment is configured, responsive to the relative currentlevels in the primary 202 and secondary 213 coils, to alter the value(e.g., the capacitance) of the passive element 212 (e.g., variablecapacitor) so that the ratio of current between the primary 202 andsecondary 213 coils is at a value that corresponds to a desired plasmadensity profile within the chamber 210. Although not shown, the controlportion 226 may include a man-machine interface (e.g., display and inputcontrols) to enable a user to receive feedback and facilitate control ofthe plasma 108.

Referring next to FIG. 3, shown is another embodiment in which thepassive termination element is implemented in a separate housing(separate from the match and controller) in close proximity with achamber. The components in the present embodiment operate in asubstantially similar manner as the components depicted in FIG. 2, butthe passive element 312 may be implemented as a separate appliance ormay be integrated with the chamber 310.

Referring next to FIG. 4, it is a flowchart depicting steps that may betraversed in connection with the embodiments described with reference toFIGS. 1-3 for controlling the spatial distribution of plasma in aprocessing chamber (e.g., chamber 110, 210). As depicted, when power isapplied (e.g., directly applied by generator 104, 204 via match) to aprimary inductor (e.g., the primary coil 102, 202), a plasma in thechamber is excited (Block 402). In addition, the primary inductor isinductively coupled to each of N (N is equal to or greater than one)secondary conductors (e.g., secondary coils L_(1-N), 213) through theplasma (Block 404), and each of the N secondary inductors is terminatedsuch that substantially all current that passes through each of the Nsecondary inductors results from mutual inductance through the plasmawith the primary inductor (Block 406). As previously discussed, thecurrent through each of the N secondary inductors affects the spatialdistribution of the plasma. Although not required, in some variations,the current through the N secondary inductors is regulated so as toregulate the spatial distribution of the plasma (Block 408).

In conclusion, the present invention provides, among other things, amethod, system, and apparatus that enables controllable plasma densitywith an actively driven coil and one or more passively terminatedinductors. Those skilled in the art can readily recognize that numerousvariations and substitutions may be made in the invention, its use, andits configuration to achieve substantially the same results as achievedby the embodiments described herein. Accordingly, there is no intentionto limit the invention to the disclosed exemplary forms. Manyvariations, modifications, and alternative constructions fall within thescope and spirit of the disclosed invention.

What is claimed is:
 1. A method for controlling a spatial distributionof plasma in a processing chamber that includes a primary inductor and Nsecondary inductors, comprising: exciting the plasma in the processingchamber with the primary inductor; inductively coupling the primaryinductor to each of N secondary inductors through the plasma, wherein Nis equal to or greater than one; and terminating each of the N secondaryinductors such that substantially all current that passes through eachof the N secondary inductors results from mutual inductance through theplasma with the primary inductor, the current through each of the Nsecondary inductors affecting the spatial distribution of the plasma. 2.The method of claim 1, wherein terminating each of the N secondaryinductors includes passively terminating each of the N secondaryinductors.
 3. The method of claim 1, including regulating currentthrough the N secondary inductors so as to regulate the spatialdistribution of the plasma.
 4. The method of claim 3, whereinterminating includes terminating each of the N secondary inductors withan impedance-adjustable termination element, and regulating currentthrough the N secondary inductors includes regulating the current byadjusting an impedance of each of the impedance-adjustable terminationelements.
 5. The method of claim 4, including: sensing at least oneparameter indicative of plasma density in regions proximal to the Nsecondary inductors, and adjusting the impedance of theimpedance-adjustable termination elements responsive to the sensing. 6.The method of claim 5, including sensing current in each of the Nsecondary inductors, and adjusting the impedance of theimpedance-adjustable termination elements by adjusting a capacitance ofthe impedance-adjustable termination elements.
 7. A system forcontrolling a spatial distribution of plasma in a processing chamberthat includes a primary inductor and N secondary inductors, comprising:means for exciting the plasma in the processing chamber with the primaryinductor; means for inductively coupling the primary inductor to each ofN secondary inductors through the plasma, wherein N is equal to orgreater than one; and means for terminating each of the N secondaryinductors such that substantially all current that passes through eachof the N secondary inductors results from mutual inductance through theplasma with the primary inductor, the current through each of the Nsecondary inductors affecting the spatial distribution of the plasma. 8.The system of claim 7, wherein the means for terminating each of the Nsecondary inductors includes means for passively terminating each of theN secondary inductors.
 9. The system of claim 7, including means forregulating current through the N secondary inductors so as to regulatethe spatial distribution of the plasma.
 10. The system of claim 9,wherein the means for terminating includes means for terminating each ofthe N secondary inductors with an impedance-adjustable terminationelement, and the means for regulating current through the N secondaryinductors includes means for adjusting an impedance of each of theimpedance-adjustable termination elements.
 11. The system of claim 10,including: means for sensing at least one parameter indicative of plasmadensity in regions proximal to the N secondary inductors, and means foradjusting the impedance of the impedance-adjustable termination elementsresponsive to the sensing.
 12. The system of claim 11, including meansfor sensing current in each of the N secondary inductors, and means foradjusting a capacitance of the impedance-adjustable terminationelements.